1. Field of the Invention
The present invention relates to a thin-film magnetic head having at least an induction-type magnetic transducer for writing and a method of manufacturing the thin-film magnetic head.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought with an increase in surface recording density of a hard disk drive. A composite thin-film magnetic head has been widely used, which is made of a layered structure including a recording head having an induction-type magnetic transducer for writing and a reproducing head having a magnetoresistive (MR) element for reading. MR elements include an anisotropic magnetoresistive (AMR) element that utilizes the AMR effect and a giant magnetoresistive (GMR) element that utilizes the GMR effect. A reproducing head using an AMR element is called an AMR head or simply an MR head. A reproducing head using a GMR element is called a GMR head. An AMR head is used as a reproducing head whose surface recording density is more than 1 gigabit per square inch. A GMR head is used as a reproducing head whose surface recording density is more than 3 gigabits per square inch.
Methods for improving the performance of a reproducing head include replacing an AMR film with a GMR film and the like made of a material or a configuration having an excellent magnetoresistive sensitivity, or optimizing the MR height of the MR film. The MR height is the length (height) between the air-bearing-surface-side end of an MR element and the other end. The MR height is controlled by an amount of lapping when the air bearing surface is processed. The air bearing surface is the surface of a thin-film magnetic head that faces a magnetic recording medium and may be called a track surface as well.
Performance improvements in a recording head have been expected, too, with performance improvements in a reproducing head. One of the factors determining the recording head performance is the throat height (TH). The throat height is the length (height) of portions of the two pole layers facing each other with a recording gap layer in between, from the air-bearing-surface-side end to the other end. A reduction in throat height is desired in order to improve the recording head performance. The throat height is controlled as well by an amount of lapping when the air bearing surface is processed.
It is required to increase the track density on a magnetic recording medium in order to increase the recording density as one of the performance characteristics of a recording head. To achieve this, it is required to implement a recording head of a narrow track structure wherein the width on the air bearing surface of a bottom pole and a top pole sandwiching the recording gap layer is reduced to the micron or submicron order. Semiconductor process techniques are employed to achieve the narrow track structure.
Reference is now made to FIG. 13A to FIG. 18A and FIG. 13B to FIG. 18B to describe an example of a method of manufacturing a composite thin-film magnetic head as a related-art method of manufacturing a thin-film magnetic head. FIG. 13A to FIG. 18A are cross sections each orthogonal to the air bearing surface of the thin-film magnetic head. FIG. 13B to FIG. 18B are cross sections of a pole portion of the head each parallel to the air bearing surface.
In the manufacturing method, as shown in FIG. 13A and FIG. 13B, an insulating layer 102 made of alumina (Al2O3), for example, having a thickness of about 5 μm is deposited on a substrate 101 made of aluminum oxide and titanium carbide (Al2O3—TiC), for example. On the insulating layer 102 a bottom shield layer 103 made of a magnetic material of 2 to 3 μm in thickness is formed for making a reproducing head.
Next, as shown in FIG. 14A and FIG. 14B, on the bottom shield layer 103, alumina, for example, is deposited to a thickness of 70 to 100 nm through sputtering to form a bottom shield gap film 104 as an insulating layer. On the bottom shield gap film 104 an MR film having a thickness of tens of nanometers is formed for making an MR element 105 for reproduction. Next, on the MR film a photoresist pattern is selectively formed where the MR element 105 is to be formed. The photoresist pattern is formed into a shape that facilitates lift-off, such as a shape having a T-shaped cross section. Next, with the photoresist pattern as a mask, the MR film is etched through ion milling, for example, to form the MR element 105. The MR element 105 may be either a GMR element or an AMR element. Next, on the bottom shield gap film 104, a pair of electrode layers 106 having a thickness of tens of nanometers are formed, using the photoresist pattern as a mask. The electrode layers 106 are electrically connected to the MR element 105.
Next, a top shield gap film 107 having a thickness of 70 to 100 nm is formed as an insulating layer on the bottom shield gap film 104 and the MR element 105. The MR element 105 is embedded in the shield gap films 104 and 107.
Next, as shown in FIG. 15A and FIG. 15B, on the top shield gap film 107, a top shield layer-cum-bottom pole layer (called a bottom pole layer in the following description) 108 having a thickness of about 3 to 3.5 μm is formed. The bottom pole layer 108 is made of a magnetic material and used for both a reproducing head and a recording head. Next, on the bottom pole layer 108, a recording gap layer 109 made of an insulating film such as an alumina film whose thickness is 0.2 to 0.3 μm is formed.
Next, as shown in FIG. 16A and FIG. 16B, a portion of the recording gap layer 109 is etched to form a contact hole 119 to make a magnetic path. On the recording gap layer 109, a photoresist layer 110 for determining the throat height is formed into a specific pattern whose thickness is about 2 μm. Next, on the photoresist layer 110, a thin-film coil 112 of a first layer is made for the induction-type recording head. The thickness of the thin-film coil 112 is about 2 μm.
Next, as shown in FIG. 17A and FIG. 17B, a photoresist layer 113 is formed into a specific pattern on the photoresist layer 110 and the coil 112. On the photoresist layer 113, a thin-film coil 114 of a second layer is then formed into a thickness of about 2 μm. Next, a photoresist layer 115 is formed into a specific pattern on the photoresist layer 113 and the coil 114. Heat treatment is then performed at a temperature of about 250° C. to flatten the surface of the photoresist layer 115.
A hill-like raised portion made up of the coils 112 and 114 and the photoresist layers 110, 113 and 115 is called an apex. The slope of the apex on the side of the air bearing surface is called an apex angle. The apex angle is generally about 45 to 55 degrees. A recording track is formed by fabricating a top pole layer on the apex.
Next, as shown in FIG. 18A and FIG. 18B, a top pole layer 116 having a thickness of about 0.5 to 1.0 μm is formed for the recording head on the recording gap layer 109 and the photoresist layers 113 and 115. The top pole layer 116 is made of a magnetic material such as Permalloy (NiFe) or FeN as a high saturation flux density material. The top pole layer 116 is in contact with the bottom pole layer 108 and magnetically coupled to the bottom pole layer 108 through the contact hole 119.
Next, the recording gap layer 109 and part of the bottom pole layer 108 are etched through ion-milling, for example, using the top pole layer 116 as a mask. Next, an overcoat layer 117 of alumina, for example, is formed to cover the top pole layer 116. The top surface of the overcoat layer 117 is flattened and pads (not shown) for electrodes are formed on the overcoat layer 117. Finally, machine processing of the slider is performed to form the air bearing surfaces of the recording head and the reproducing head. The thin-film magnetic head is thus completed. As shown in FIG. 18B, the structure is called a trim structure wherein the sidewalls of the top pole layer 116, the recording gap layer 109, and part of the bottom pole layer 108 are formed vertically in a self-aligned manner. The trim structure suppresses an increase in the effective track width due to expansion of a magnetic flux generated during writing in a narrow track.
FIG. 19 is a top view of the thin-film magnetic head manufactured as described above. The overcoat layer 117 is omitted in FIG. 19. As shown in FIG. 19, the top pole layer 116 has a pole portion 116a placed on a side of an air bearing surface 120 and a yoke portion 116b placed in a position facing the coils 112 and 114. The width of the pole portion 116a defines the recording track width. Part of the yoke portion 116b closer to the pole portion 116a tapers down to the pole portion 116a. The periphery of the tapered portion forms an angle of 45 degrees, for example, with a surface parallel to the air bearing surface 120. In FIG. 19 a numeral 108a indicates the portion where the bottom pole layer 108 is etched to form the trim structure.
In the following description the position of the air-bearing-surface-side end of the insulating layer is called a zero throat height position and indicated with TH0.
In order to achieve high surface density recording, it has been required that the recording track width, that is, the pole portion width (called pole width in the following description) is reduced. The pole portion having a width of the submicron order such as 0.5 μm or less is desired. One of the techniques that have been used for implementing such a reduced pole width is to divide the top pole layer into a pole portion and a yoke portion.
As disclosed in Japanese Patent Application Laid-open Hei 7-262519 (1995), for example, frame plating may be used as a method for fabricating the top pole layer. In this case, a thin electrode film made of Permalloy, for example, is formed by sputtering, for example, to fully cover the apex, that is, the hill-like raised portion of the coil. Next, a photoresist is applied on the electrode film and patterned through a photolithography process to form a frame to be used for plating. The top pole layer is then formed by plating through the use of the electrode film previously formed as a seed layer.
However, there is a difference in height between the apex and the other part, such as 7 to 10 μm or more. The photoresist whose thickness is 3 to 4 μm is applied to cover the apex. If the photoresist thickness is required to be at least 3 μm over the apex, a photoresist film having a thickness of 8 to 10 μm or more, for example, is formed below the apex since the fluid photoresist goes downward.
To implement a recording track width of the submicron order as described above, it is required to form a frame pattern of the submicron order through the use of a photoresist film. When the top pole layer is divided into a pole portion and a yoke portion, it is required to form not only the pole portion but also the yoke portion of the submicron order, too, if the recording track width of the submicron order is formed. Therefore, it is required to form a fine pattern of the submicron order through the use of a photoresist film having a thickness of 8 to 10 μm or more. However, it is extremely difficult to form a photoresist pattern having such a thickness into a reduced pattern width in a manufacturing process.
Furthermore, rays of light used for exposure of photolithography are reflected off the base electrode film as the seed layer. The photoresist is exposed to the reflected rays as well and the photoresist pattern may be out of shape. It is therefore impossible to obtain a sharp and precise photoresist pattern.
As thus described, it is difficult in related art to fabricate the top pole layer with accuracy if the pole width of the submicron order is required. In the case where the top pole layer is divided into the pole portion and the yoke portion, too, it is difficult to form the yoke portion with accuracy in the position corresponding to the pole portion.
For a thin-film magnetic head having surface recording density as high as 5 to 10 GB per square inch, for example, a throat height of 0.6 to 0.9 μm and a recording track width of 0.7 to 1.0 μm (the effective magnetic track width is 0.8 to 1.2 μm) are required. However, due to the above-stated reason, it is difficult in related art to control the pole width to be 0.7 to 1.0 μm (the effective magnetic track width is 0.8 to 1.2 μm).
In the related art, as shown in FIG. 19, the interface region between the pole portion 116a and the yoke portion 116b of the top pole layer 116, that is, the region where the width of the top pole layer 116 changes, is located closer to the apex than zero throat height position THO. This is because it is difficult to form the wide yoke portion 116b on the slope of the apex. The reason will now be described. If the yoke portion 116b which is greater than the recording track in width is formed on the slope of the apex, it is required that the width of the top pole layer 116 is abruptly changed at the base of the apex from the greater width of the yoke portion 116b to the width equal to the recording track width of the submicron order. However, it is impossible to change the width in this way if the top pole layer 116 is formed through photolithography. This is because, when exposure is performed for photolithography, the rays of light reflected off the slope of the apex make it impossible to obtain a precise photoresist pattern at the base of the apex. In the related art, since the base of the apex is located at zero throat height position TH0, it is impossible to abruptly change the width of the top pole layer 116 at zero throat height position TH0. It is possible to precisely control the width of the pole portion 116a at a point 1 to 2 μm closer to the air bearing surface 120 than zero throat height position TH0.
Therefore, in the related art the throat height is increased and it is impossible to improve properties such as the overwrite property required for writing data over data already written on a recording medium, the nonlinear transition shift (NLTS), the writing property called flux rise time that indicates the rise time of a magnetic field.
In the related art the interface region between the pole portion 116a and the yoke portion 116b of the top pole layer 116 is located closer to the apex than zero throat height position TH0. Consequently, the volume of the top pole layer 116 near zero throat height position TH0 is not enough. The magnetic flux is therefore saturated near zero throat height position TH0 and the flux does not fully reach the tip of the pole portion. As a result, if the recording track width is 0.8 μm (the effective track width is 1.0 μm), for example, the value indicating the overwrite property is as low as 15 to 20 dB. It is therefore impossible to achieve an optimal overwrite property. In general, the overwrite property is required to be about 25 to 35 dB.
In the related-art thin-film magnetic head, the photoresist layer surrounding the coil defines the throat height. However, the photoresist layers of a plurality of head elements formed in one wafer are not precisely and uniformly aligned. The principal reason is that, since the photoresist layers expand when heat treatment is performed or the photoresist layers that define the throat heights are etched, too, when the seed layers of the coils are etched through ion milling, it is difficult to align the ends of the photoresist layers of a plurality of head elements in a row. The variation in alignment of a plurality of head elements in a row is 0.2 to 0.5 μm at most.
Therefore, in the related art, if the throat height of the submicron order is required, the yield is greatly reduced, due to variations in throat heights of head elements, when the air bearing surface of a bar separated from a wafer and including a row of head elements is lapped.
In Japanese Patent Application Laid-open Hei 8-87717 (1996) a thin-film magnetic head is disclosed for increasing recording track density. In the head a tip of an insulating layer on which a coil is formed is located at least 3 μm away from the zero throat height position toward a rear gap (a portion in which top and bottom pole layers are in contact with each other). Alternatively, the start point of the coil is located at least 10 μm away from the zero throat height position. However, in these structures the magnetic path length is increased, and it is impossible to achieve sufficient intensity of the write magnetic field and gradient of rise of the field with respect to time when the frequency of data to write is high. The properties of the head is thereby reduced.